(1) Field of the Invention
The present invention relates to a flat-panel television and audio equipment, more particularly, to audio equipment, which outputs an error signal when an abnormal operation occurs, and a flat-panel television provided with the audio equipment.
(2) Description of Related Art
A flat-panel television apparatus includes, for example, audio equipment, which outputs a sound from a speaker based on a sound signal that is input in an audio output amplifier IC. Some type of this audio output amplifier IC outputs a high signal as an error signal when abnormalities, such as output short, thermal shutdown, reduced voltage detection, and instantaneous interruption detection, for example, occur. It is well known that such an error signal is used for a countermeasure against heating or the like for protecting the audio output amplifier IC and other devices when an abnormal operation occurs, by shutting off the power supplied to the audio equipment to turn off the power of the flat-panel television apparatus when the high signal is output.
FIG. 3 is a schematic diagram showing an example of a portion related to shutting off the power that is supplied to the audio equipment when an abnormal operation occurs in the flat-panel television apparatus. In FIG. 3, a power supply circuit 1 is a partial resonance power supply circuit; it converts an external power, for example, a commercial AC power into a plurality of types of predetermined voltages, and outputs the operating power voltages to all portions of the flat-panel television apparatus. Audio equipment 2 comprises mainly an audio output amplifier IC 2a that outputs a sound from a speaker 2b based on an audio signal and a constant voltage circuit 2c that output a constant voltage to the audio output amplifier IC 2a. This audio output amplifier IC 2a outputs a high signal as an error signal when abnormalities, such as output short, thermal shutdown, reduced voltage detection, and instantaneous interruption detection, for example, occur. When the high signal is continuously input for a predetermined time, a microcomputer 3 judges that the system is in an abnormal state, and outputs an OFF signal Poff in place of an ON signal Pon as a signal to order ON/OFF of the power supply circuit 1. Thereby, the power supply circuit 1 is turned off, and the outputs of all the operating voltages are stopped, enabling to protect the audio output amplifier IC and other parts from heating due to the abnormal state.
Japanese Unexamined Patent Application Publication No. Hei7 (1995)-78941, discloses a system of an overheat protection circuit by means of a semiconductor integrated circuit (IC), wherein it includes a shutoff circuit that stops the operations of a temperature monitoring circuit and other main circuits in the IC chip according to the output of the detected temperature, and the shutoff circuit includes a timer circuit section, whereby the system judges whether or not the signal of the temperature monitoring circuit is high for more than a predetermined time, and stops the operation of the main circuit after judging that the signal is high for more than a predetermined time.
Japanese Unexamined Patent Application Publication No. Hei7 (1995)-13643 discloses a system of an overheat protection circuit, wherein it does not output a shutoff signal even if a malfunction occurs in the shutoff circuit when it turns on or off the power under a high temperature condition due to the degradation of the heat dissipation efficiency.
Japanese Unexamined Patent Application Publication No. 2000-47848 discloses an audio output control system, wherein it automatically returns to the normal operation without performing any external manipulations even if the sound synthesis IC runs out of control.
In addition, in Japanese Unexamined Patent Application Publication No. 2002-150723, there is disclosed a signal processing unit of audio equipment comprising: a multi-channel decoder (MCD) or a digital interface receiver (DIR), a digital signal processor (DSP), and a microcomputer as an integrated circuit (IC); wherein a forcible mute circuit, which acts like an AND circuit by forcibly zeroing the output signal of the DSP according to the error detection data that is output from the MCD or DIR and muting the circuit, is provided in the latter part of the DSP.
Hereby, in order to prevent the control operation at the abnormal state from becoming unstable as far as possible due to the effect of noise or the like, and due to the phenomenon that the error signal oscillates irregularly between high (H) and low (L) caused by such as the load short and the short between pins in the IC or other similar devices, it is normally carried out to turn off the power by judging that the system is in an abnormal state when the error signal remains a high signal for a predetermined time as described above.
Therefore, because the system is not judged as an abnormal state and the power is not turned off when a halfway abnormal operation occurs such as when the signal oscillates between high (H) and low (L) caused by such as the load short and the short between pins in the IC or other similar devices, it was necessary to take measures against heating by assuming the heating beforehand when such the halfway abnormal operation occurred. For example, it was necessary to decrease the temperature by providing a radiation plate so that the heating temperature becomes lower than a prescribed value even if the power consumption is increased or by increasing the resistance value of a resistor 2d as shown in FIG. 3 so that the resistor can withstand even if the power consumption is increased. Such measures against heating were an excess quality except when the halfway abnormal operation occurs, and could cause the cost up of the system. Effective measures against heating when the halfway abnormal operation occurs have not been proposed yet.